Microwave power divider/combiners achieve higher microwave power levels by dividing microwave input power among plural amplifier circuits whose outputs are then combined to yield a greater balanced total output power. The splitting and combining may be accomplished by a coupler. A 3 dB hybrid coupler (2-way) has four ports and can be used, for example, to combine or sum the power at the two input ports to provide twice the power at a third or output port. The fourth port produces an output that is the difference between the two input ports and is terminated in a 50 ohm line. A 6 dB hybrid coupler (4-way) has eight ports and can be used, for example, to combine or sum the power at the four input ports to provide four times the power at a fifth or output port. The remaining three ports are terminated in 50 ohm lines. Similarly, when used as a splitter a 2-way coupler couples one-half of the power transmitted by an input transmission line to each of a pair of output transmission lines, and 4-way splitter couples one-fourth of the power at an input port to each of four output ports.
A stripline coupler generally has two quarter wave length conductors or strips running parallel in an enclosed square shaped cavity with the conductors terminating in right angle bends. One of the problems with such couplers is that discontinuities are introduced by the right angle bends. These bends cause a mismatch in the even-mode and odd-mode impedances resulting in an imbalance between the input and output ports of the coupler. In the prior art, these discontinuities were compensated by means of capacitive tuning screws or by placing tuning stubs-on the conductors. A typical design with such compensation is discussed in Microwave Filters, Impedance-Matching Networks, and Coupling Structures; G. Matthaei, L. Young, E. M. T. Jones; Artech House, Inc., 1964; pp. 793-797. This prior art approach requires precise positioning and dimensional tolerances, making the parts expensive because of the required mechanical accuracy and the machining difficulties.